The present invention relates to a sheet cutter for cutting or partially cutting a sheet such as straight paper, rolled paper, folded paper and a film, at a desired length or desired portion leaving partially the sheet uncut in a printer, a ticket vending machine, a facsimile machine or the like.
In one of conventional sheet cutters of such kind, a saw-like cutting member is put into a groove as disclosed in the Japanese Utility Model Publication No. 45276/79. Another one of the conventional sheet cutters has scissors-like construction.
In the conventional sheet cutter whose saw-like cutting member is put into the groove, the sharp cutting edge of the member is penetrated into a sheet. The groove only acts to hold the sheet, and no sharp cutting edge is provided at the groove. The sharpness of the cutting edge of the saw-like member is necessary to stably cut the sheet. If the cutting edge is worn due to the use thereof or the chips or dust of the sheet deposits in the troughs between the cutting teeth of the saw-like cutting member, the member is likely to push the sheet into the groove without cutting it.
The usable life of the cutting member is known to be likely to become short at the innermost portions of the troughs, because (1) the tips of the teeth of a grinding stone for sharpening the cutting teeth of the saw-like cutting member come into contact with the member at the innermost portions of the troughs so that the tips are much worn to make it difficult to sharpen the cutting edges of the member at the innermost portions of the troughs, (2) the chips or dust made at the time of the cutting of the sheet is likely to deposit in the innermost portions of the troughs, and (3) the sheet is easily folded into the groove at the cutting by the troughs, at which the sheet is mostly cut, in case that the cutting resistance increases due to the wear of the cutting edges of the cutting member, the deposition of the chips or dust, or the like. In the cutter using the saw-like cutting member, since the usable life of the saw-like cutting member is usually short, the cutter has a disadvantage that the cutting member needs to be often cleaned or replaced.
In the conventional sheet cutter having a scissors-like construction, a sheet is cut between the cutting edges of a pair of cutting members. For that reason, even if the cutting edges are not very sharp or are slightly worn, they can cut the sheet. Besides, the cutting members do not have troughs in which the chips or dust of the sheet is likely to deposit as in those of the saw-like cutting member. As a result, the usable life of the cutting members of the sheet cutter is longer than that of the saw-like cutting member. The difference in the length of the period of usability is also understood from the fact that the cutting edge of a kitchen knife needs to be often sharpened but those of scissors do not need to be often sharpened.
The stroke of the saw-like cutting member of the conventional sheet cutter can be optionally controlled to either cut the sheet or only make a perforation therein, as described in the above-mentioned Publication. However, since the conventional sheet cutter having the scissors-like constitution cuts the sheet in such a manner that the cutting edges of the pair of cutting members are gradually overlapped with each other from one end of each of the cutting edges to the other thereof, it is difficult to leave partially the sheet uncut. Although the pair of cutting members can be stopped halfway to partially cut the sheet to leave a portion thereof uncut, the sheet partially cut in that way is more likely to be torn off than a sheet having a perforation.